1. Field of the Invention
The present invention relates to a retarder for setting of gypsum and a process for setting gypsum. More particularly, the present invention is concerned with a retarder containing a carboxyalkylated protein as the active component thereof for use in setting of gypsum and an effective process for setting gypsum by the use of the retarder.
2. Description of the Prior Art
Gypsum, particularly hemihydrate gypsum is widely used in construction material, pottery material, etc., and those hemihydrate gypsums commercially available on the market produced by calcination usually contain anhydrous gypsum and gypsum dihydrate. Molding of such hemihydrate gypsum, however, has been quite difficult on account of the high setting speed of the paste thereof. Therefore, in molding gypsum for various kinds of uses, keratin type animal proteins such as gelatin, or citric acid or its salts have hitherto been added as retarders for setting of gypsum, thereby reducing the setting speed of gypsum and increasing workability such as molding, etc.
However, where the above described animal protein is used as a retarder for setting of gypsum, the disadvantages occur in that it has a poor solubility in cold water, it is putrefactive and that the strength of the set gypsum decreases with an increase in the amount of the animal protein added. Furthermore, its retarding effect is not sufficient and the supply of the animal protein has often been limited.
Recently, a retarder composed mainly of whey derived from soybean, cotton seed, sunflower, etc., (Japanese Patent Laid Open No. 143819/1975), a retarder composed mainly of water-soluble lower peptide obtained by treating a protein with an acid, alkali or protein decomposing enzyme (Japanese Patent Laid Open No. 143818/1975), a retarder composed mainly of a water-soluble condensate prepared by reacting an amino acid and an aldehyde (Japanese Patent Laid Open No. 143818/1975), etc., have been developed. With these retarders, however, only insufficient retarding effect is obtained and the disadvantage occurs in that a reduction in the strength of the set gypsum is great.